Telephone system having two-party lines



TELEPHONE SYSTEM HAVING TWO-PARTY LINES Filed Ma rch :5, 19:58

TB @114 qrAa e I) /N Vrv Patented July 25, 1939 PATENT OFFICE TELEPHONE. SYSTEM HAVING TWO-PARTY LINES Harald Valdemar Alexandersson and Otto Georg Reinhold Siewert, Stockholm, Sweden, assignors to Telcfonaktiebolaget L. M. Ericsson, Stockholm, Sweden, a company of Sweden Application March 3, 1938. Serial No. 193,758 In Sweden April23, 1936 1 Claim.

The present invention relates to telephone systems having two-party lines, and relates more particularly to telephone systems of this kind provided with a central battery. In such systems it has been difiicult to find a simple arrangement of the party lines which, while permitting of the setting up of connections between the two subscribers belonging to the same party line, insures secrecy of the calls. This problem has been solved through the present invention, however, which comprises the provision, for each one of the two subscribers sets connected to a party line, of a relay which is connected in series with the set and in parallel with a half-wave rectifier r in such a manner that on talking connections between the two sets the relay will remain unactuated whereas on a call between one of the subscribers and a subscriber outside the party line the relay will disconnect the other one of the subscribers sets connected to the party line.

The invention will now be described more in detail having reference tothe drawing attached to this specification and forming part thereof, which drawing shows an example of a two-party line connected to a manual telephone exchange.

Referring to the drawing, A and B are the two subscribers sets which are connected over a party line PL to a telephone exchange. The subscribers sets are fed with current from a central battery in the exchange. Each subscribers set is equipped in ordinary manner with a microtelephone MI or M2, a telephone receiver PI or P2, a speaking transformer ICI or 102 and a bell RKI or RK2. To each subscribers set is allotted a relay RA or RB, which is connected in parallel with a rectifier I5 or IE in such a manner that the relay will operate only for a certain current direction. Provided in the telephone exchange are, among others, two relays RI and R2, a jack J, and three push buttons TA, TB and TAB.

Upon a call from one of the subscribers, for example the subscriber A, the following switching operations will take place. When the subscriber, by lifting off his micro-telephone, actuates the switch hook KLI, the contact I I will be closed, a calling circuit I2 being then completed over the party line PL, through the relays RA and RI. The current in the circuit I2 has such a direction that the rectifier I5, which is connected in parallel with the relay RA, does not pass any current. Consequently, the whole current will pass through the relay RA which operates and disconnects at its contact I3, I4 the subscribers set B from the party line PL. On operation of the relay RI provided in the exchange the lamp L is lighted due to the closing of the relay contact [1. The operator now inserts a plug in the jack J, causing the relay R2 to be energized over a contact I8. On'operation the relay R2 interrupts at its contact I9 the current through the lamp. If the call is intended for another subscriber than the subscriber B, the connection can now be completed in ordinary manner. If, on the other hand, the subscriber A desires to be connected to the subscriber B belonging to the same party line, the operator must first press the push-button TB in order to be able to effect the setting up of the connection. The pressing of the push-button TB causes the circuit I2 to be interrupted and the relay RA to drop its armature, rendering it possible to send a ringing signal over a contact 2I closed by the push-button TB, and one branch of the party-line, and the switch hook KL2 to the earthed bell RKZ of the subscriber B. During the ringing period the relay RB operates and disconnects the subscribers set A. On release of the push-button TB by the operator the ringing signal will cease. The operator thereafter pushes the button TAB. The current feed relay RI of the exchange will then be connected to the party-line TL, so that the direction of the current in the line TL will now be opposite to the direction of the current upon a call, resulting in that neither the relay RA nor the relay RB can attract its armature, in that for the direction of the current now set up both of said relays-will be shunted by the appertaining rectifiers I5 and. I6. When the subscriber B has answered the call both of the subscribers A and B will be in talking connection with each other over condensers C3, C4 connected in parallel with the relays RA and RB. During the conversation between said subscribers the operator can remove the plug, the relay R2 being held energized over a contact 22 provided on the push-button TAB. As soon as the conversation has been finished and the microtelephones replaced on the switch-hooks the relay RI will drop its armature, the lamp L being then ignited because of current supplied over contacts 23 of the relay R2. When thereafter the operator pulls out the button TAB, the relay R2 will be deenergized and the lamp goes out.

A call to one of the subscribers A or B coming from the telephone exchange is put through un- 55 der co-operation of the operator. After a plug has been inserted in the jack J a ringing signal can be transmitted to the wanted subscriber A, B by depressing the proper one of the ringing buttons TA and TB. As soon as the called sub- 55 scriber answers, the corresponding relay BA or RB respectively will attract its armature and disconnect the other subscriber. When after completed conversation the microtelephone of the party-line subscriber is put back on the switchhook the relay RI is de-energized and the lamp L is lit, whereupon the operator releases the connection.

In the embodiment illustrated in the drawing the two-party line arranged according to the invention is connected to a manual telephone exchange. However, the invention can be realized also in connection with automatic telephone exchanges. The reversal of the direction of the current in the party line TL which is'efiected in the illustrated embodiment by the operator by means of the button TAB can be efiected in an automatic system by means of a relay which isactuated from a device operated by the numerical impulses, for example: a selector, a register or a follow-up device when the calling subscriber A has dialled the number of the subscriber B connected to the same line.

We claim: 7

In a telephone system having two party lines connected to a central battery, a relay individual to each subscriber branch line and connected in series with said branch line, each of said relays adapted when energized to disconnect the other subscriber branch line, a half-wave rectifier connected in parallel with each of said relays and so directed that the current normally sent from the central battery during a conversation between'one of the two party line subscribers and a subscriber outside the party line actuates said relay, and means for reversing the direction of the current during a connection between the two subscribers of the same party line.

HARALD VALDEMAR. ALEXANDERSSON.

O-TTO GEORG REINHOLD SIEWERT. 

